In this specification, a number of documents including patent applications and manufacturer's manuals are cited. The disclosure of these documents, while not considered relevant for the patentability of the present invention, is herewith incorporated by reference in its entity. More specifically, all the referenced documents are incorporated by reference to the same extent as if each individual document was specifically and individually indicated to be incorporated by reference.
All current biotechnological concepts and methods for the biosynthesis of 1,2-propanediol(PD) utilize the naturally occurring pathway via methylglyoxal which suffers from significant drawbacks as follows: (i) the generation of the highly toxic intermediate methylglyoxal; (ii) reduced efficiency under anaerobic and microaerobic conditions due to higher energetic burden for the cell; and (iii) the fact that it is difficult to achieve optimal control of cell metabolism due to fermentation requirements.
U.S. Pat. No. 6,087,140, WO 1999028481 and U.S. Pat. No. 6,303,352 describe the biosynthesis of PD from sugars with a genetically engineered microorganism expressing a recombinant methylglyoxal synthetase and other enzymatic activities. The described processes utilize the mentioned natural pathway via dihydroxyaceton phosphate and methylglyoxal.
WO 2011012697, WO 2011012702, WO 2011012693, WO 2005073364, US 2007072279, WO 2008116852, WO 2008116853, EP 2192180 and US 2010261239 also propose utilization of the natural PD biosynthesis pathway via dihydroxyaceton phosphate and methylglyoxal, with various modifications to enhance efficacy of this pathway.
WO 2010012604 specifically proposes the utilization of glycerol as carbon source for PD production, in a recombinant microorganism expressing enzymes such as glycerol dehydrogenase (gldA), dihydroxyacetone kinase (dhaK), methylglyoxal synthase (mgsA) or propanediol oxidoreductase (fucO), which are all part of the natural pathway via dihydroxyaceton phosphate and methylglyoxal.
U.S. Pat. No. 7,049,109 describes the utilization of Klebsiella pneumoniae to produce PD from sugars. This strain is a natural PD producer, presumably utilizing the methylglyoxal pathway.
Unrelated to current PD biosynthesis pathways, but integral part of the pathway presented in this invention, is an enzyme with lactate CoA-transferase activity, as has been described (Selmer et al., 2002, Eur. J. Biochem. 269: 372-380). The conversion of lactate to lactoyl-CoA through lactate CoA-transferase/propionate CoA-transferase is occurring naturally, more specifically in the pyruvate fermentation pathway found in microorganisms such as Clostridium propionicum (Cardon et al., 1947, Archives of Biochemistry & Biophysics 12: 165-171) or Megasphaera elsdenii (Baldwin et al., 1965, Biochim Biophys Acta 97: 202-13). There, lactate is converted via lactoyl-CoA and acrylyl-CoA to propanoyl-CoA and finally to propionate, the end product.
In view of the deficiencies of the processes described in the art, the technical problem underlying the present invention can be seen in the provision of alternative or improved means and methods for producing propanediol and compounds related thereto.